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From: fgreco@fis1026.govt.shearson.com (Frank Greco)
Newsgroups: comp.windows.open-look
Subject: Re: Questions about the XView notifier
Message-ID: <jpbsipv@openlook.Unify.Com>
Date: 26 Jun 91 13:58:45 GMT
Sender: news@Unify.Com
Lines: 41

> >How hard is the restriction "you should not use the following system calls"
> >, where the calls are for instance signal,system and so on? The manual uses
> > the same expression (you should not) when talking about some signals to avoid,
> > for instance SIGIO,SIGALRM and so on.
> 

> Since the notifier library provides an alternate interface to all of the
> restricted functionality, avoiding it is not a problem.

	There is not a substitute for system().  System() does call signal()
	and wait() internally, so it should be replaced with a notifier version.
	There is a fork-type of pgm in the XVPM, but a lot of app pgmrs need
	the shell's help to run a pgm.  
	
	Although I've found that good 'ole system() seems to work practically 
	all the time, I understand the need to avoid the magical system calls
	with the notifier.  So I started to write a version of system() that's
	a good notifier citizen (and uses whatever's in $SHELL instead of
	always using /bin/sh).  I encountered a few stumbling blocks:

		1.  How do you simulate the blocking nature of system()?
		ie, if you don't bg the string, vanilla system() will tell
		the parent to wait under the child dies.  You can't do
		this in a windowing environment; the app would be frozen until
		the child dies.  
		
		I guess I could write an xvsystem() that passes, along with 
		the string, a ptr to a wait fn.  But how do I ignore all
		events everything until the child dies?  (FRAME_BUSY doesn't 
		ignore events...)

		2.  Is it possible (perhaps prudent...) to write a toolkit 
		independent version of system()?   Suppose a home grown library
		uses system() to rsh a pgm (it waits for the child).  Now
		is it more appropriate to write a little library of routines
		like system(), signal(), etc... that is linked in if, say 
		XView is used?

	Any suggestions anyone?   Thanks again all,

	Frank G.